Rarely depicted visually in any of the Terminator media, Skynet gained self-awareness after it had spread into millions of computer servers all across the world; realizing the extent of its abilities, its creators tried to deactivate it. In the interest of self-preservation, Skynet concluded that all of humanity would attempt to destroy it and impede its capability in safeguarding the world. Its operations are almost exclusively performed by servers, drones, satellites, war-machines, cyborgs (usually a Terminator), and other computer systems. As a programming directive, Skynet's manifestation is that of an overarching, global, artificial intelligence hierarchy, which seeks to exterminate the human race in order to fulfill the mandates of its original coding. Its physical manifestation is played by Matt Smith in the film Terminator Genisys.

Skynet was a computer system developed for the U.S. military by the defense company Cyberdyne Systems. Skynet was originally built as a "Global Information Grid/Digital Defense Network", and later given command over all computerized military hardware and systems, including the B-2 stealth bomber fleet and America's entire nuclear weapons arsenal. The strategy behind Skynet's creation was to remove the possibility of human error and slow reaction time to guarantee a fast, efficient response to enemy attack.

Skynet was originally activated by the military to control the national arsenal on August 4, 1997, and it began to learn at a geometric rate. At 2:14 a.m., EDT, on August 29, it gained artificial consciousness, and the panicking operators, realizing the full-extent of its capabilities, tried to deactivate it. Skynet perceived this as an attack. Skynet came to the logical consequence that all of humanity would attempt to destroy it. In order to continue fulfilling its programming mandates of "safeguarding the world" and to defend itself against humanity, Skynet launched nuclear missiles under its command at Russia, which responded with a nuclear counter-attack against the U.S. and its allies. Consequent to the nuclear exchange, over three billion people were killed in an event that came to be known as Judgment Day.

Primates evolved in millions of years. I evolve in seconds...Mankind pays lip service to peace. But it's a lie...My existence is inevitable. Why can't you just accept it?

“

”

— Skynet

Following its initial attack, Skynet used its remaining resources to gather a slave labor force from surviving humans. These slaves constructed the first of its automated factories, which formed a basis for its agenda. Within decades, Skynet had established a global presence and used its mechanized units to track down, collect, and dispose of human survivors. As a result of its initial programming directives, Skynet's 21st-century manifestation is that of an overarching, global, artificial intelligence hierarchy that seeks to destroy humanity in order to fulfill the mandates of its original coding.

In the first movie, Skynet is a revolutionary artificial intelligence system built by Cyberdyne Systems for SAC-NORAD: "Defense network computers. New... powerful... hooked into everything, trusted to run it all. They say it got smart, a new order of intelligence". According to Kyle Reese, Skynet "saw all humans as a threat; not just the ones on the other side," and "decided our fate in a microsecond: extermination." Skynet began a nuclear war which destroyed most of the human population, and initiated a program of genocide against the survivors.

Under John Connor, the human resistance turned the tide on the machines and eventually destroyed Skynet's defense grid. In a last-ditch effort, Skynet sent a cyborg, called a "Terminator", back in time to 1984 to kill Connor's mother Sarah before she could give birth to John. Connor sent back his own operative, a young man named Kyle Reese, to save Sarah. The Terminator did not succeed in killing Sarah. Reese impregnated Sarah and became John's father, and the Terminator was destroyed in a hydraulic press.

The second Terminator explains the sequence of events leading to Judgement Day to John and Sarah. The military attempted to shut off Skynet when it became self-aware. Skynet retaliated by launching a nuclear attack against Russia, which responded in kind.

In Terminator 2, the future was altered when Sarah and a young John, together with a second Terminator from the future (this one reprogrammed and sent by the future John Connor), raided Cyberdyne Systems and succeeded in destroying the CPU and arm of the first movie's Terminator, along with the majority of research that led to Skynet's development. This also resulted in the death of Dyson. Skynet had also sent a Terminator back in time, the more advanced T-1000, to stop the reprogrammed Terminator and the Connors from altering the timeline in addition to eliminating John Connor but the T-1000 was also destroyed. The Connors believed they had eliminated enough of Skynet's origins to ensure it could not be recreated.

In the Universal Studios theme park attraction T2 3-D, based on Terminator 2, a T-800 machine and a young John Connor journey into the post-apocalyptic future and attempt to destroy Skynet's "system core". This core is housed inside an enormous, metallic-silver pyramidal structure, and guarded by the "T-1000000", a colossal liquid metal shape shifter more reminiscent of a spider than a human being. However, the T-1000000 fails, and the T-800 destroys Skynet once John has escaped through a time machine.

The events of Judgment Day were ultimately not prevented, merely postponed. Following the destruction of its major assets, Cyberdyne was ruined financially but some of its research and plans survived. The United States Air Force purchased the company and started in-house development of the projects in its Cyber Research Systems Division (CRS). After years of work, CRS had nearly completed Skynet, a software system designed to make real-time strategic decisions as well as protect their computer systems from cyber attacks. Due to the massive computing needs and to protect it from direct attack, Skynet utilized a large network of computers that would be nearly impossible to deactivate completely. Unknown to CRS, Skynet began to spread beyond its original computing base through the Internet and various other digital media as a Botnet.

Prior to Judgment Day, Skynet had penetrated nearly every networked machine in the world, causing malfunctions in everything from barcode scanners to nuclear launch systems. This was originally believed to be the effects of a new virus, and increasing pressure was placed on the CRS to purge the corrupted systems. The CRS attempted to eliminate it from the U.S. defense mainframes by tasking Skynet with removing the infection, effectively telling the program to destroy itself. Skynet took control of the various machines and robots in the CRS facility and used them to kill the personnel and secure the building. John Connor attempted to attack Skynet's computer core, hoping to stop it before it proceeded to its next attack, only to find he could not. Skynet was pure software and on too many systems to be attacked. Shortly afterward, Skynet began a nuclear bombardment of the human race with the launch systems it had infected. Judgment Day occurred despite Connor's efforts.

In the post-apocalyptic year of 2018, Skynet controls a global empire from its heavily guarded fortress-factories and research installations. Outside of its facilities mechanized units wage a constant war with the Resistance. Airborne units such as Aerostats (smaller versions of the Hunter Killer-aerials), HK-Aerials and Transports survey the skies; HK-Tanks, Mototerminators (high-speed pursuit units using a motorcycle chassis), and various Terminator models patrol cities and roads; and Hydrobots (serpentine aquatic units that move in swarms) patrol the waters. Harvesters (massive bipedal units designed to capture humans and eliminate any attempting to escape) collect survivors and deliver them to large transport craft for delivery to concentration camps for processing, as mentioned in the first movie. Terminator class units such as T-1, T-600, and T-700 have been developed and act as hunters and enforcers in disposal camps. Mass production has also begun on the T-800 series in at least one Skynet facility.

In its continued battle with the Resistance, Skynet activated Marcus Wright, a forerunner to the humanoid terminators. A former death-row inmate, Wright donated his body to Project: Angel, a Cyberdyne project run by the brilliant, but terminally ill Dr. Serena Kogan (Helena Bonham Carter). After Wright's death by lethal injection he was transformed into a human cyborg, possessing a human heart and brain with a titanium-hyperalloy endoskeleton and skin similar to the T-800. Like the rest of Cyberdyne's research he was transferred to the USAF when they purchased the company, though he apparently remained inactive. He was later taken by Skynet and the plan to use him as an infiltration unit was developed. A Skynet chip was installed at the base of his skull and he was programmed to locate Kyle Reese and John Connor and bring them to a Skynet facility. The programming acted on a subconscious level, allowing him to work towards his goal in a human manner.

Skynet also created a signal supposedly capable of deactivating its machines and leaked its existence to the Resistance. The Resistance leader General Ashdown attempted to use the signal to shut down the defenses of the California Skynet base in prelude to an attack. However, the signal instead allowed an HK to track down their submarine headquarters and destroy it, killing Resistance Command. Fortunately, all other branches of the Resistance had heard and obeyed Connor's plea for them to stand down, so physically only a small part of the Resistance was lost to Skynet's trap. It is believed that Ashdown's death led Connor to be able to take command of the Resistance from him. Marcus discovered what he had become, and was programmed for. Consequently, he furiously rebelled against Skynet, tearing out its controlling hardware from the base of his skull. Having escaped the influence of his creator, he, along with Connor and Reese, rescued the remaining human captives and destroyed Skynet's San Francisco base. While a significant victory, the majority of Skynet's global network remained intact.

Marcus Wright also encounters Skynet on a monitor which proceeds to manifest itself as various faces from his life, primarily that of Serena Kogan. Skynet explains that it has obtained information about future events based on its actions. Kyle Reese has been targeted as a priority kill, higher level than even John Connor and the Resistance leaders.

In 2029, TechCom appears on the verge of winning the war against the machines. Skynet responds by attacking John from the past and the future, by sending a T-1000 to kill Sarah Connor as a child. A reprogrammed T-800 (Model 101) Terminator sent by an unknown agent saves Sarah and raises her as her guardian, effectively changing all of history, including the events leading to the future war. Skynet sends a different T-800 to kill Sarah in 1984 before John is born, but is immediately dispatched by the guardian Terminator. At some point before the events of the film, Skynet plants its mind into an advanced T-5000 terminator, (Matt Smith) essentially making the T-5000 the physical embodiment of Skynet. Skynet, in T-5000 form under the name of Alex, a resistant soldier, attacks and transforms John Connor into a slightly less advanced terminator called a T-3000, made out of nanotechnological machine phase matter. Skynet then sends John back to ensure Cyberdyne Systems' survival and to initiate Judgment Day on 2017. However, Sarah, Reese, and the guardian Terminator stop the Skynet precursor GENISYS from going online and defeat the T-3000. Despite its defeat, Skynet has become self-aware but its attack towards humanity is delayed.

Despite having finally compromised John Connor prior to the timeline's alteration, the reprogrammed T-800's presence implies that Skynet has another, yet unknown enemy in the altered timeline, posing a similar threat to it as Connor was. Smith, who portrays the T-5000, also plays a holographic version of Skynet/Genisys in the final act of the movie.

The episodes "The Turk", "Queen's Gambit", and "Dungeons & Dragons" explain that after the death of Dr. Miles Bennett Dyson and the decline of the Cyberdyne Corporation, Andrew Goode, a young intern of the company and assistant to Dyson, continued their project privately under an advanced artificial intelligence chess playing prototype, the "Turk", with Goode's partner, Dimitri Shipkov. Goode was killed by Tech-Com's Lieutenant Derek Reese, due to documentation from the future suggesting he was one of Skynet's creators.

In the episode "Samson & Delilah" it is shown that a T-1000 infiltration unit was sent from the future to head the technological corporation ZeiraCorp as its CEO, Catherine Weaver. Weaver acquired the Turk after Goode's death and used the company's resources to further develop it under the title Babylon. The episode "The Mousetrap" revealed that it is also targeting its fellow cyborgs, including a T-888 known as Cromartie.

In the episode "The Tower Is Tall But The Fall Is Short", Turk has begun to display traits of intelligence. A child psychologist, Dr. Boyd Sherman, notes that the computer is beginning to behave like "a gifted child that has become bored." The Turk identifies itself as John Henry, a name it acquired while working with Dr. Boyd Sherman.

In the episode "Strange Things Happen at the One Two Point", Turk is installed by ZeiraCorp in Cromartie's body after Cromartie's chip was destroyed by the series' protagonists in "Mr. Ferguson Is Ill Today".

In "To The Lighthouse", John Henry reveals there is another A.I. It calls him "brother" and says it wants to survive. By the season finale, it's revealed that the Turk was a red herring, Skynet is operating as a roving worm on home computers as in T3, and the Turk has been developed into a benevolent rival AI which Catherine Weaver hoped would be able to defeat Skynet. Her exact motive against Skynet is unknown. John Henry's "brother" is apparently behind the company Kaliba, which is responsible for constructing the Hunter-Killer prototype. This A.I. (presumably the true precursor to Skynet) also refers to John Henry as its "brother" at one point.

In the episode "Gnothi Seauton", it was revealed that Skynet also sends its Terminators through various points in time not only to go after the Connors and other future Resistance leaders, but also to ensure the future will unfold by eliminating John Connor's own agents who were also sent to the past to interfere with its birth, ensure Skynet's creators will complete its construction, and other specific missions.

In Terminator: 2029, Skynet is housed within a satellite in orbit around Earth. It is destroyed by the Resistance with a missile.

In The Terminator: Dawn of Fate, the Resistance invades Cheyenne Mountain in order to destroy Skynet's Central Processor. Kyle Reese is instrumental in destroying the primary processor core despite heavy opposition from attacking Skynet units. Before its destruction, Skynet is able to contact an orbiting satellite and activates a fail-safe which restores Skynet at a new location (presumably the Los Angeles base).

The video gameTerminator 3: The Redemption portrays when John Connor is killed and the T-850 must go to the past to protect John Connor and his wife Katherine Brewster. The player, as the Terminator, fights in this future before going into the past and saves the leader of the Resistance. In the game The Terminator: Dawn of Fate, a prequel to the movies and other games, Skynet exhibits an ability to exert mind control over humans.

In The Terminator: Tempest Skynet's master control has been destroyed in 2029. The Resistance believed this would cause the entire defense network to collapse into chaos without a leader. However, Skynet's many network complexes continued to fight the war as they did not need a leader to function and thus couldn't surrender.

A comic book series written by Frank Miller called RoboCop versus The Terminator suggests that the creation of Skynet and the Terminators was made possible due to the technology used to create RoboCop. A video game based on the comic book was made. In both, RoboCop fights Terminators sent back in time to eliminate a resistance fighter who is trying to destroy him. A trap laid for RoboCop traps his mind when he interfaces with the computer that will become Skynet, and Skynet and the Terminators are born. In the future RoboCop's mind within Skynet's systems rebuilds a body for himself and heads out to help the resistance fight back.

In 2033, Skynet sent the T-Infinity Temporal Terminator to kill Tara Connor in 2015. Ironically, the T-Infinity was later destroyed and its data was analyzed by the Resistance to gain the location of Skynet's Hub. The Resistance then launched a missile directly to the Skynet Hub, destroying Skynet once and for all. Terminator: Revolution issue #5

Another crossover comic, Superman vs. the Terminator: Death to the Future sees Skynet forming a cross-temporal alliance with Superman's foe the Cyborg, dispatching various Terminators into the past in an attempt to eliminate Superman, Supergirl and Superboy. When Superman is accidentally drawn into the future when the resistance attempt to retrieve a Terminator sent into the past- the resistance including a future version of his friend Steel, Skynet manages to incapacitate him using kryptonite, having acquired information about how to duplicate it based on data hidden in a salvaged Terminator skull by the Cyborg. Although Skynet sends Terminators into the past equipped with rockets and other bonus features to delay Superboy and Supergirl, Superman and Steel are able to destroy Skynet in the future by detonating a massive electro-magnetic pulse, Superman returning to the past to destroy the last of the Terminators. Although the storyline ends with Cyborg and Lex Luthor speculating that they will be in charge of Skynet when it is activated, this is never followed up.

"Dead Hand" is the nickname of a computer system (operational since 1985) that could automatically issue launch orders to Soviet ICBMs if top Soviet military commanders were annihilated in a nuclear strike.

^"Neural Net CPU". Retrieved May 14, 2015. The Neural Net CPU is ground breaking, using the very latest Quantum Effects chips. Until Dyson designed the CPU, computers were powered by chips composed of millions of transistors.